Field of the Invention
The present invention relates to an edge termination for a semiconductor component formed of silicon carbide and to a Schottky diode having an edge termination. The present invention also relates to a method for producing a semiconductor component having such an edge termination.
The invention relates predominantly to asymmetrically blocking semiconductor components having planar edge terminations. The invention relates in particular to semiconductor components in the form of Schottky diodes. Such semiconductor components and their method of operation have been known for a long time and require no further description.
In semiconductor components of such a type, in particular in the case of high-voltage-resistant power semiconductor components, voltage breakdowns preferably occur in the edge area, since the electrical field strength there is particularly large owing to the curvature of the doped regions as a result of the edge. In order to avoid such voltage breakdowns, edge terminations are provided, which are disposed in the form of rings and typically completely enclose the semiconductor component. The edge terminations weaken or reduce local field strength peaks in the edge area of the semiconductor component. Undesirable voltage breakdowns in the edge area can thus be avoided, and the semiconductor component remains serviceable. A large number of different edge terminations for semiconductor components are described in a reference by B. J. Baliga, titled "Modern Power Devices", John Wiley and Sons, 1987.
Furthermore, U.S. Pat. No. 5,486,718 describes edge terminations in which chains of zener diodes containing polysilicon are disposed in a spiral shape in the edge area. These zener diodes are intended to control the potential profile of the electrical field in the edge area.
On page 437 of the reference titled "Modern Power Devices", mentioned above, edge terminations for Schottky diodes are described. Here, one of the edge terminations is in the form of a guard ring that surrounds the Schottky contact and forms a pn-junction with the remaining semiconductor region. Alternatively, the Schottky contact can also be provided directly with an edge termination formed from field plates, that is to say without a pn-junction.
Schottky diodes are majority-carrier semiconductor components and are thus particularly suitable for high-frequency applications, that is to say for applications which require very fast switching processes and a reverse current which is as low as possible during off-commutation. Silicon Schottky diodes are, however, limited to reverse voltages of about 100 V owing to their very large reverse current.
Thus, for these reasons, it is becoming ever more attractive to use other semiconductor materials, which do not have the disadvantages mentioned above, to produce Schottky diodes.
One such material, for example, is silicon carbide (SiC). U.S. Pat. No. 5,789,311 describes an SiC Schottky diode. SiC semiconductor components and SiC Schottky diodes have excellent electrical and physical characteristics in comparison with those semiconductor components produced from silicon, and a number of these will be described in the following text.
The breakdown field strength of SiC is greater than that of silicon by a factor of 10 to 15. Owing to the very high breakdown field strength, SiC semiconductor components can be made very small, which advantageously also results in a very low ON resistance. SiC semiconductor components thus offer a particularly good compromise between a high blocking capability and a low forward voltage.
Owing to the fact that SiC has a considerably shorter charge carrier life than silicon, SiC is particularly suitable for semiconductor components for radio-frequency applications, since considerably higher switching speeds can be achieved here. Owing to the fact that an SiC Schottky diode has virtually no minority charge carriers, the charge carriers can be depleted very quickly during off-commutation, thus making high switching speeds possible.
In comparison to silicon, SiC is thermally extremely stable-SiC has a sublimation temperature of more than 1600.degree. C.--and its thermal conductivity is greater by a factor of 3. Particularly owing to the fact that SiC has a very wide energy gap and, associated with this, a low intrinsic concentration, SiC is particularly suitable for applications at high temperatures.
A major disadvantage of semiconductor components composed of SiC is, however, that high temperatures (&gt;1500.degree. C.) are typically required to heal and activate implanted doped regions, and these high temperatures generally do not allow such SiC semiconductor components to be processed in conventional workshops set up for silicon technology.